title: Theoretical studies of the quinolinic acid to nicotinic acid mononucleotide transformation.
abstract: Quinolinate phosphoribosyl transferase (QPRTase) is an essential enzyme that catalyzes the transformation of quinolinic acid (QA) to nicotinic acid mononucleotide (NAMN), a key step on the de novo pathway for nicotinamide adenine dinucleotide (NAD) biosynthesis. We describe herein a theoretical study of the intrinsic energetics associated with the possible mechanistic pathways by which QA forms NAMN. Our main interest is in probing the decarboxylation step, which is intriguing since the product is a vinylic anion, not unlike the reaction catalyzed by orotidine 5'-monophosphate (OMP) decarboxylase, an enzyme whose mechanism is under fierce debate. Our calculations indicate that a path involving a quinolinic acid mononucleotide (QAMN) intermediate is the most energetically attractive, favoring decarboxylation. We also find that the monocarboxylate form of QAMN will decarboxylate much more favorably energetically than will the dicarboxylate form of QAMN. Furthermore, our calculations indicate that decarboxylation is not a likely first step; the substrate in such a mechanism would prefer to decarboxylate at the C3 position, not the desired C2 position. We also discuss our results in the context of existing experimental data.
authors.affiliation: Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854, USA.
authors.forename: Aleksandr
authors.initials: A
authors.lastname: Rozenberg
authors.forename: Jeehiun K
authors.initials: JK
authors.lastname: Lee
mesh_terms: D002244:Carbon / Q000737:chemistry; D002245:Carbon Dioxide / Q000737:chemistry; D002625:Chemistry, Organic / Q000379:methods*; D019295:Computational Biology / Q000379:methods; D003653:Decarboxylation; D008956:Models, Chemical; D008962:Models, Theoretical; D009243:NAD / Q000737:chemistry; D009537:Nicotinamide Mononucleotide / Q000031:analogs & derivatives* / Q000737:chemistry; D009964:Orotidine-5'-Phosphate Decarboxylase / Q000737:chemistry; D017378:Quinolinic Acid / Q000737:chemistry*; D012984:Software; D012997:Solvents / Q000737:chemistry; D013816:Thermodynamics
chemical_list: D012997:Solvents; D009243:NAD; D009537:Nicotinamide Mononucleotide; D002245:Carbon Dioxide; C002953:nicotinate mononucleotide; D002244:Carbon; D009964:Orotidine-5'-Phosphate Decarboxylase; D017378:Quinolinic Acid